For many applications in high speed communication technology stable clock signals are needed that show random jitter contents below limits specified in the applying standards. Examples for these applications are clock and data recovery circuits and synthesizers for wireless communication links.
To meet the jitter requirements of the applying standards oscillator circuits are needed that generate clock signals which containing the least possible amount of phase noise. Furthermore it is desirable to implement all necessary functionality as a monolithic integrated circuit (IC) to lower the power dissipation, the part count and the space needed for the circuitry (and thus reducing costs).
Therefore efforts have been made to integrate LC-tank type oscillators on monolithic integrated circuits. This type of oscillator shows a significantly better phase noise performance than so called ring oscillators, which are widely used for integrated circuits. This is due to the properties of the LC-tank, which offers a steep phase response versus frequency at its resonant frequency and therefore supports a stable oscillation. However, the supporting circuitry such as bias and supply voltage regulators have to be carefully designed, since noise injected into the LC-tank type oscillator by this circuitry can significantly degrade the phase noise performance.